Fix attempt to create ValueType from void type in ForwardMethodBuilder

Bug: 183734568
Change-Id: I9239c0299dbfddd77226c2c800a0a5bb838067de
diff --git a/src/main/java/com/android/tools/r8/ir/synthetic/ForwardMethodBuilder.java b/src/main/java/com/android/tools/r8/ir/synthetic/ForwardMethodBuilder.java
index 48536cc..4a24a4b 100644
--- a/src/main/java/com/android/tools/r8/ir/synthetic/ForwardMethodBuilder.java
+++ b/src/main/java/com/android/tools/r8/ir/synthetic/ForwardMethodBuilder.java
@@ -291,7 +291,9 @@
       assert !sourceMethod.getReturnType().isVoidType();
       assert targetMethod.getReturnType().isVoidType();
       assert invokeType == InvokeType.SPECIAL;
-    } else if (castResult) {
+    } else if (castResult
+        && !sourceMethod.getReturnType().isVoidType()
+        && !targetMethod.getReturnType().isVoidType()) {
       assert ValueType.fromDexType(sourceMethod.getReturnType())
           == ValueType.fromDexType(targetMethod.getReturnType());
     } else {